Although major depression and alcohol dependence co-occur commonly, the pathophysiologic basis for this comorbidity is poorly understood. This study examines the role of serotonin (5-HT) in producing depressive symptoms in alcoholics. A total of 40 depressed alcoholics in remission from both disorders will undergo two laboratory sessions in random order. During these sessions they will ingest an amino acid mixture containing all amino acids on one day, and all amino acids with the exception of tryptophan (TRP) on a second occasion one week later. Due to the stimulation of protein synthesis, TRP, the precursor of 5-HT, is depleted when the amino acid load containing no TRP is administered. It is hypothesized that depressed alcoholics will show a transient increase in depressive symptoms due to TRP depletion.